Re: [csswg-drafts] [css-border][css-animation][css-transition] Animations/Transitions of border-width after change of computed value definition in issue #11494 (#13511)

> [@weinig](https://github.com/weinig) I don't think that's what's going on, at least in your reduced test-case (https://bug-307933-attachments.webkit.org/attachment.cgi?id=478378).
> 
> We use computed values to trigger transitions. It just so happens that the initial value of `border-*-width` is `medium`, so your reduced test-case doesn't change `border-width` at all?

That test case is indeed slightly different from what I described here, but I am still seeing something in Firefox than I would expect if only computed value was being observed. 
- In Firefox (and in older WebKit), I see it smoothly animating the border and background color. 
- In tip-of-tree WebKit, and what I would expect if only computed value was being observed, I see it smoothly animating the background color, and then popping in a border at the 50% mark (when border style changes from none to solid).

I just uploaded a second test case, https://bug-307933-attachments.webkit.org/attachment.cgi?id=478391, which is more like the described scenario, and in Firefox I see it only animating the background color.

-- 
GitHub Notification of comment by weinig
Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/13511#issuecomment-3917629914 using your GitHub account


-- 
Sent via github-notify-ml as configured in https://github.com/w3c/github-notify-ml-config

Received on Tuesday, 17 February 2026 23:36:13 UTC